Earphones have been widely applied in people's daily life and work. Besides the functions of enjoying music and entertainments, earphones are also widely applied to insulate noise for maintaining a relatively quiet environment. However, for low-frequency noises, earphones are very limited in the effect and capability of noise insulation.
An active noise-reduction technology adopts an approach of generating a signal having a same amplitude but an inverse phase relative to an external noise so as to counteract the noise entering into an earphone. However, the active noise-reduction technologies adopted in current earphone are mostly fixed noise-reduction technologies, which have the following defects: in a constantly changing external environment, when the external noise is equivalent to a fixed noise-reduction amount, a relatively good noise-reduction effect will be generated; however, when the external noise is higher than the fixed noise-reduction amount, it will occur that the noise-reduction effect cannot be optimal; or when the external noise is lower than the fixed noise-reduction amount, an active noise-reduction module will actually produce a new noise into human ears.